In semiconductor processing technology, planar substrate surfaces which are horizontal with respect to a wafer surface are patterned by photolithographic methods in combination with selective etching processes. During the processing of integrated circuits, reliefs with a pronounced topography are formed on the wafer or substrate surface. Typically, this type of relief includes surfaces which are inclined or vertical with respect to the substrate surface. As sizes of integrated circuits continue to shrink, it is becoming more and more necessary to pattern vertical or inclined device surfaces so as to functionally differentiate these devices over their vertical extent while still maintaining pattern alignment. Examples of these types of semiconductor devices include deep trench capacitors, stacked capacitors, and vertical transistors.
Currently, it is not possible to put patterns directly on walls which are vertical with respect to the substrate surface using conventional photolithographic techniques. Usually, vertical wall patterning of this nature is accomplished using a suitable filler material which, when partially filling in a trench, acts as a mask for the portions of the wall located underneath while allowing for processing of the walls above the filler material. For example, when an oxide is to be deposited exclusively on vertical walls below a filler material, the oxide is first deposited or produced over the entire surface of the relief. The relief or trench is initially completely filled with a suitable filler material. Then, the filler material is recessed back to a depth that just covers the desired oxide. After uncovered sections of the oxide are removed, the remaining filler material is removed.
Alternatively, when an oxide is to be deposited or produced only in upper regions of a vertical wall, an etching stop layer, for example, a nitride layer is first provided over the entire surface of the entire relief pattern. A different material, susceptible to directional etching, for example, polycrystalline silicon, is used to fill the relief, and is etched back as far as the desired coverage depth of the final vertical oxide. After the etching stop layer is removed from the unfilled sections of the walls, an oxide is deposited or generated using a thermal technique in the uncovered regions. Next, the oxide is anisotropically etched which removes the deposited oxide from horizontal. This is followed by removal of the filler material and, then, the removal of the etching stop layer.
There are deposition processes which can be used to deposit thin films on vertical or inclined surfaces of a substrate relief. However, it is difficult to control the thickness of the layer deposited. Typically, the thickness of the coating decreases as the depth of the relief increases, for example, as the length of the vertical or inclined wall increases. As such, layers deposited using these types of deposition processes have considerable differences in thickness over the length of the relief. These types of deposition processes include plasma-enhanced chemical vapor deposition (PECVD) and diffusion-limited deposition of silicon oxide using tetraethyl orthosilicate (TEOS).
High current semiconductor devices manufactured by techniques capable of producing small device features by using vertical or inclined walls have been produced. In some cases, the resulting devices comprise two electrodes, one serving as a gate and another as either a source or a drain electrode, positioned in a manner to create a parasitic capacitor by the overlap between them. In the more common planar devices, the problem of overlap can be solved by such techniques as self-aligned gates. In vertical architectures, a high precision alignment to the vertical wall can reduce the amount of overlap in some cases.
A need exists, however, for manufacturing techniques for semiconductor devices comprising vertical or inclined walls that do not require high precision alignments that reduce the overlap capacitance between electrodes. There is also a need to provide processes with fewer steps, to reduce the time and cost of manufacture.